Prior maintenance systems have included arrangements for monitoring the status of plug-in circuit boards. The circuit board status includes its operational states, e.g., inserted and operating properly, whether or not requesting service not inserted, or loss of power or other failure. These prior arrangements typically used multiple wires to communicate the circuit board status to a central control unit or the like. If a single wire was used, there was no way of distinguishing between a circuit board failure and a circuit board removal.
Indeed, the number of input/output (I/O) pins/signals on a plug-in circuit board is limited. Therefore, it is desirable to employ a single wire solution to minimize the number of I/O pins/signals that are needed to communicate the status of the circuit board to the central control unit.